The 5.8.9 release will be the last significant release of the 5.8.x series.
Any future releases of 5.8.x will likely only be to deal with security issues,
and platform build failures.
Hence you should look to migrating to 5.10.x,
if you have not started already.
See "Known Problems" for more information.

A particular construction in the source code of extensions written in C++ may need changing.
See "Changed Internals" for more details.
All extensions written in C,
most written in C++,
and all existing compiled extensions are unaffected.
This was necessary to improve C++ support.

Other than this,
there are no changes intentionally incompatible with 5.8.8.
If any exist,
they are bugs and reports are welcome.

It is now possible to call stat and the -X filestat operators on directory handles.
As both directory and file handles are barewords,
there can be ambiguities over which was intended.
In these situations the file handle semantics are preferred.
Both also treat *FILE{IO} filehandles like *FILE filehandles.

It's possible to enhance the mechanism of subroutine hooks in @INC by adding a source filter on top of the filehandle opened and returned by the hook.
This feature was planned a long time ago,
but wasn't quite working until now.
See "require" in perlfunc for details.
(Nicholas Clark)

The constant folding routine is now wrapped in an exception handler,
and if folding throws an exception (such as attempting to evaluate 0/0),
perl now retains the current optree,
rather than aborting the whole program.
Without this change,
programs would not compile if they had expressions that happened to generate exceptions,
even though those expressions were in code that could never be reached at runtime.
(Nicholas Clark,
Dave Mitchell)

The code that caches calculated UTF-8 byte offsets for character offsets for a string has been re-written.
Several bugs have been located and eliminated,
and the code now makes better use of the information it has,
so should be faster.
In particular,
it doesn't scan to the end of a string before calculating an offset within the string,
which should speed up some operations on long strings.
It is now possible to disable the caching code at run time,
to verify that it is not the cause of suspected problems.

This variable gives the native status returned by the last pipe close,
backtick command,
successful call to wait or waitpid,
or from the system operator.
See perlvar for details.
(Contributed by Gisle Aas.)

This variable controls the state of the internal UTF-8 offset caching code.
1 for on (the default),
0 for off,
-1 to debug the caching code by checking all its results against linear scans,
and panicking on any discrepancy.

Perl 5.8.9 (and 5.10.0 onwards) now provides a couple of macros to do very basic exception handling in XS modules.
You can use these macros if you call code that may croak,
but you need to do some cleanup before giving control back to Perl.
See "Exception Handling" in perlguts for more details.

The interpreter internals now support a far more memory efficient form of inlineable constants.
Storing a reference to a constant value in a symbol table is equivalent to a full typeglob referencing a constant subroutine,
but using about 400 bytes less memory.
This proxy constant subroutine is automatically upgraded to a real typeglob with subroutine if necessary.
The approach taken is analogous to the existing space optimisation for subroutine stub declarations,
which are stored as plain scalars in place of the full typeglob.

However,
to aid backwards compatibility of existing code,
which (wrongly) does not expect anything other than typeglobs in symbol tables,
nothing in core uses this feature,
other than the regression tests.

Stubs for prototyped subroutines have been stored in symbol tables as plain strings,
and stubs for unprototyped subroutines as the number -1,
since 5.005,
so code which assumes that the core only places typeglobs in symbol tables has been making incorrect assumptions for over 10 years.

Perl 5.8.9 adds a new utility perlthanks, which is a variant of perlbug, but for sending non-bug-reports to the authors and maintainers of Perl. Getting nothing but bug reports can become a bit demoralising - we'll see if this changes things.

The default since perl 5.000 has been for perl to create an empty scalar with every new typeglob. The increased use of lexical variables means that most are now unused. Thanks to Nicholas Clark's efforts, Perl can now be compiled with -DPERL_DONT_CREATE_GVSV to avoid creating these empty scalars. This will significantly decrease the number of scalars allocated for all configurations, and the number of scalars that need to be copied for ithread creation. Whilst this option is binary compatible with existing perl installations, it does change a long-standing assumption about the internals, hence it is not enabled by default, as some third party code may rely on the old behaviour.

We would recommend testing with this configuration on new deployments of perl, particularly for multi-threaded servers, to see whether all third party code is compatible with it, as this configuration may give useful performance improvements. For existing installations we would not recommend changing to this configuration unless thorough testing is performed before deployment.

diagnostics no longer uses $&, which results in large speedups for regexp matching in all code using it.

Regular expressions classes of a single character are now treated the same as if the character had been used as a literal, meaning that code that uses char-classes as an escaping mechanism will see a speedup. (Yves Orton)

Creating anonymous array and hash references (ie. [] and {}) now incurs no more overhead than creating an anonymous list or hash. Nicholas Clark provided changes with a saving of two ops and one stack push, which was measured as a slightly better than 5% improvement for these operations.

Many calls to strlen() have been eliminated, either because the length was already known, or by adopting or enhancing APIs that pass lengths. This has been aided by the adoption of a my_sprintf() wrapper, which returns the correct C89 value - the length of the formatted string. Previously we could not rely on the return value of sprintf(), because on some ancient but extant platforms it still returns char *.

index is now faster if the search string is stored in UTF-8 but only contains characters in the Latin-1 range.

The Unicode swatch cache inside the regexp engine is now used. (the lookup had a key mismatch, present since the initial implementation). [RT #42839]

There is now Configure support for creating a relocatable perl tree. If you Configure with -Duserelocatableinc, then the paths in @INC (and everything else in %Config) can be optionally located via the path of the perl executable.

At start time, if any paths in @INC or Config that Configure marked as relocatable (by starting them with ".../"), then they are prefixed the directory of $^X. This allows the relocation can be configured on a per-directory basis, although the default with -Duserelocatableinc is that everything is relocated. The initial install is done to the original configured prefix.

Configure is now better at removing temporary files. Tom Callaway (from RedHat) also contributed patches that complete the set of flags passed to the compiler and the linker, in particular that -fPIC is now enabled on Linux. It will also croak when your /dev/null isn't a device.

A new configuration variable d_pseudofork has been to Configure, and is available as $Config{d_pseudofork} in the Config module. This distinguishes real fork support from the pseudofork emulation used on Windows platforms.

Config.pod and config.sh are now placed correctly for cross-compilation.

$Config{useshrplib} is now 'true' rather than 'yes' when using a shared perl library.

Starting with Solaris 10, we do not want versioned shared libraries, because those often indicate a private use only library. These problems could often be triggered when SUNWbdb (Berkeley DB) was installed. Hence if Solaris 10 is detected set ignore_versioned_solibs=y.

Many many bugs related to the internal Unicode implementation (UTF-8) have been fixed. In particular, long standing bugs related to returning Unicode via tie, overloading or $@ are now gone, some of which were never reported.

unpack will internally convert the string back from UTF-8 on numeric types. This is a compromise between the full consistency now in 5.10, and the current behaviour, which is often used as a "feature" on string types.

Internally, perl object-ness is on the referent, not the reference, even though methods can only be called via a reference. However, the original implementation of overloading stored flags related to overloading on the reference, relying on the flags being copied when the reference was copied, or set at the creation of a new reference. This manifests in a bug - if you rebless an object from a class that has overloading, into one that does not, then any other existing references think that they (still) point to an overloaded object, choose these C code paths, and then throw errors. Analogously, blessing into an overloaded class when other references exist will result in them not using overloading.

The implementation has been fixed for 5.10, but this fix changes the semantics of flag bits, so is not binary compatible, so can't be applied to 5.8.9. However, 5.8.9 has a work-around that implements the same bug fix. If the referent has multiple references, then all the other references are located and corrected. A full search is avoided whenever possible by scanning lexicals outwards from the current subroutine, and the argument stack.

A certain well known Linux vendor applied incomplete versions of this bug fix to their /usr/bin/perl and then prematurely closed bug reports about performance issues without consulting back upstream. This not being enough, they then proceeded to ignore the necessary fixes to these unreleased changes for 11 months, until massive pressure was applied by their long-suffering paying customers, catalysed by the failings being featured on a prominent blog and Slashdot.

Fixed bug RT #32539, DynaLoader.o is moved into libperl.so to avoid the need to statically link DynaLoader into the stub perl executable. With this libperl.so provides everything needed to get a functional embedded perl interpreter to run.

Fix bug RT #36267 so that assigning to a tied hash doesn't change the underlying hash.

Fix bug RT #6006, regexp replaces using large replacement variables fail some of the time, i.e. when substitution contains something like ${10} (note the bracket) instead of just $10.

threads cleanup veto has been extended to include perl_free() and perl_destruct()

On some systems, changes to $ENV{TZ} would not always be respected by the underlying calls to localtime_r(). Perl now forces the inspection of the environment on these systems.

The special variable $^R is now more consistently set when executing regexps using the (?{...}) construct. In particular, it will still be set even if backreferences or optional sub-patterns (?:...)? are used.

This new fatal error occurs when the C routine Perl_sv_chop() was passed a position that is not within the scalar's string buffer. This is caused by buggy XS code, and at this point recovery is not possible.

A more informative fatal error issued when calling dump on Win32 and Cygwin. (Given that the purpose of dump is to abort with a core dump, and core dumps can't be produced on these platforms, this is more useful than silently exiting.)

The perl sources can now be compiled with a C++ compiler instead of a C compiler. A necessary implementation details is that under C++, the macro XS used to define XSUBs now includes an extern "C" definition. A side effect of this is that C++ code that used the construction

typedef XS(SwigPerlWrapper);

now needs to be written

typedef XSPROTO(SwigPerlWrapper);

using the new XSPROTO macro, in order to compile. C extensions are unaffected, although C extensions are encouraged to use XSPROTO too. This change was present in the 5.10.0 release of perl, so any actively maintained code that happened to use this construction should already have been adapted. Code that needs changing will fail with a compilation error.

set magic on localizing/assigning to a magic variable will now only trigger for container magics, i.e. it will for %ENV or %SIG but not for $#array.

The new API macro newSVpvs() can be used in place of constructions such as newSVpvn("ISA", 3). It takes a single string constant, and at C compile time determines its length.

The new API function Perl_newSV_type() can be used as a more efficient replacement of the common idiom

sv = newSV(0);
sv_upgrade(sv, type);

Similarly Perl_newSVpvn_flags() can be used to combine Perl_newSVpv() with Perl_sv_2mortal() or the equivalent Perl_sv_newmortal() with Perl_sv_setpvn()

Two new macros mPUSHs() and mXPUSHs() are added, to make it easier to push mortal SVs onto the stack. They were then used to fix several bugs where values on the stack had not been mortalised.

A Perl_signbit() function was added to test the sign of an NV. It maps to the system one when available.

Perl_av_reify(), Perl_lex_end(), Perl_mod(), Perl_op_clear(), Perl_pop_return(), Perl_qerror(), Perl_setdefout(), Perl_vivify_defelem() and Perl_yylex() are now visible to extensions. This was required to allow Data::Alias to work on Windows.

Perl_find_runcv() is now visible to perl core extensions. This was required to allow Sub::Current to work on Windows.

ptr_table* functions are now available in unthreaded perl. Storable takes advantage of this.

There have been many small cleanups made to the internals. In particular, Perl_sv_upgrade() has been simplified considerably, with a straight-through code path that uses memset() and memcpy() to initialise the new body, rather than assignment via multiple temporary variables. It has also benefited from simplification and de-duplication of the arena management code.

A lot of small improvements in the code base were made due to reports from the Coverity static code analyzer.

Corrected use and documentation of Perl_gv_stashpv(), Perl_gv_stashpvn(), Perl_gv_stashsv() functions (last parameter is a bitmask, not boolean).

PERL_SYS_INIT, PERL_SYS_INIT3 and PERL_SYS_TERM macros have been changed into functions.

PERLSYS_TERM no longer requires a context. PerlIO_teardown() is now called without a context, and debugging output in this function has been disabled because that required that an interpreter was present, an invalid assumption at termination time.

All compile time options which affect binary compatibility have been grouped together into a global variable (PL_bincompat_options).

The values of PERL_REVISION, PERL_VERSION and PERL_SUBVERSION are now baked into global variables (and hence into any shared perl library). Additionally under MULTIPLICITY, the perl executable now records the size of the interpreter structure (total, and for this version). Coupled with PL_bincompat_options this will allow 5.8.10 (and later), when compiled with a shared perl library, to perform sanity checks in main() to verify that the shared library is indeed binary compatible.

Symbolic references can now have embedded NULs. The new public function Perl_get_cvn_flags() can be used in extensions if you have to handle them.

The core code, and XS code in ext that is not dual-lived on CPAN, no longer uses the macros PL_na, NEWSV(), Null(), Nullav, Nullcv, Nullhv, Nullhvetc. Their use is discouraged in new code, particularly PL_na, which is a small performance hit.

However, programs that rely on bugs that have been fixed will have problems. Also, many bug fixes present in 5.10.0 can't be back-ported to the 5.8.x branch, because they require changes that are binary incompatible, or because the code changes are too large and hence too risky to incorporate.

We have only limited volunteer labour, and the maintenance burden is getting increasingly complex. Hence this will be the last significant release of the 5.8.x series. Any future releases of 5.8.x will likely only be to deal with security issues, and platform build failures. Hence you should look to migrating to 5.10.x, if you have not started already. Alternatively, if business requirements constrain you to continue to use 5.8.x, you may wish to consider commercial support from firms such as ActiveState.

Win32 upgraded to version 0.38. Now has a documented 'WinVista' response from GetOSName and support for Vista's privilege elevation in IsAdminUser. Support for Unicode characters in path names. Improved cygwin and Win64 compatibility.

Steve Hay worked behind the scenes working out the causes of the differences between core modules, their CPAN releases, and previous core releases, and the best way to rectify them. He doesn't want to do it again. I know this feeling, and I'm very glad he did it this time, instead of me.

Paul Fenwick assembled a team of 18 volunteers, who broke the back of writing this document. In particular, Bradley Dean, Eddy Tan, and Vincent Pit provided half the team's contribution.

Schwern verified the list of updated module versions, correcting quite a few errors that I (and everyone else) had missed, both wrongly stated module versions, and changed modules that had not been listed.

The crack Berlin-based QA team of Andreas König and Slaven Rezic tirelessly re-built snapshots, tested most everything CPAN against them, and then identified the changes responsible for any module regressions, ensuring that several show-stopper bugs were stomped before the first release candidate was cut.

The other core committers contributed most of the changes, and applied most of the patches sent in by the hundreds of contributors listed in AUTHORS.

If you find what you think is a bug, you might check the articles recently posted to the comp.lang.perl.misc newsgroup and the perl bug database at http://bugs.perl.org. There may also be information at http://www.perl.org, the Perl Home Page.

If you believe you have an unreported bug, please run the perlbug program included with your release. Be sure to trim your bug down to a tiny but sufficient test case. Your bug report, along with the output of perl -V, will be sent off to perlbug@perl.org to be analysed by the Perl porting team. You can browse and search the Perl 5 bugs at http://bugs.perl.org/

If the bug you are reporting has security implications, which make it inappropriate to send to a publicly archived mailing list, then please send it to perl5-security-report@perl.org. This points to a closed subscription unarchived mailing list, which includes all the core committers, who will be able to help assess the impact of issues, figure out a resolution, and help co-ordinate the release of patches to mitigate or fix the problem across all platforms on which Perl is supported. Please only use this address for security issues in the Perl core, not for modules independently distributed on CPAN.